The long-term goal of our laboratory is to understand the structure and function of certain redundant genes in the fruit fly, Drosophila melanogaster, by both physical and genetic means. Our goals for the coming year include the construction of chimeric plasmids composed of pMB9 and 5S RNA genes of Drosophila melanogaster and the further characterization of 5S DNA. In addition, we have discovered a ribosomal RNA gene mutant that has a unit repeat length substantially different from that commonly observed in the wild type rRNA gene cluster. This variant occurs at a sufficiently high abundancy in the total cluster of ribosomal RNA genes such that it provides a convenient marker to follow exactly what happens during the course of rRNA gene magnification and reduction. BIBLIOGRAPHIC REFERENCES: Similarities and differences in the structure of X and Y chromosome rRNA genes of Drosophila. Tartof, K.D. and Dawid, I.B. Nature 263: 27-30, 1976. Restriction map of 5S RNA genes of Drosophila melanogaster. Procunier, J.D. and Tartof, K.D. Nature 263: 255-257, 1976.